Subject How to retrieve list of users granted with the admin role

As SYSDBA I like to know which users are granted in the past with the ADMIN ROLE (as in CREATE USER Test1 PASSWORD 'test' GRANT ADMIN ROLE).

I guess those users have the system defined RDB$ADMIN role assigned in the security database, but I do not have direct access to the security databae to check this. Also the system table SEC$USERS does not give me a clue.

Any other suggestions how to retrieve those users with admin role?